Hexagonal boron nitride (h-BN) is also known as “white graphite” due to its honeycomb lattice structure which is similar to that for graphite. Being uniquely as an insulator in the two-dimensional (2D) family and coupled with its atomic smoothness and low density of surface dangling bonds, h-BN exhibits many outstanding properties and may be used as a substrate or dielectric material for other 2D materials such as graphene, and transition metal dichalcogenides (TMDs) for various high-performance 2D heterostructure devices and next-generation 2D heterostructure electronics, protective coatings, thermal interface material, and heat spreader. Due to its ability to withstand harsh conditions, h-BN may also be used as an ultrathin encapsulation layer to prevent device degradation for materials which are more susceptible to oxidation such as black phosphorus (BP).
Motivated by industrialization and the need for manufacturability, a variety of synthesis techniques to achieve atomically thin h-BN films over large distances have been explored, such as surface segregation method, solid source diffusion, ion-beam sputtering deposition (IBSD), pulsed-laser deposition (PLD), reactive magnetron sputtering, and molecular beam epitaxy (MBE).
Traditional B-containing gaseous precursors such as boron tribromide (BBr3), boron trifluoride (BF3), boron trichloride (BCl3) and diborane (B2H6) together with N-containing gaseous precursors such as ammonia (NH3) as feedstock gases have been explored for BN film growth. However, these B-containing compounds are highly toxic which limit their applications. Therefore, exploration and development of other alternatives with relatively low toxicity and cost as well as their corresponding processes for high-quality BN film growth remain an urgent need.
Ternary films containing composites of BN and graphene domains (BNC) may be prepared using additional C-containing precursor by mixing CH4 into the reaction. Bulk amorphous, textured or nanocrystalline BNC films with thickness above 100 nm may be grown typically on Si substrates. Atomically thin highly crystalline films, however, cannot be deposited on Si or other dielectric substrates due to the lack of catalytic activity, epitaxial relation and different growth mechanisms. In this case, the growth of BN or BNC films is randomly oriented due to the uncontrolled nucleation and incomplete decomposition of the precursor.
In view of the above, there remains a need for an improved method to prepare a boron nitride material that overcomes or at least alleviates one or more of the above-mentioned problems.